/*
 * Copyright (C) 2018 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.google.common.collect;

import static java.util.Objects.requireNonNull;

import com.google.common.annotations.GwtCompatible;
import com.google.common.annotations.VisibleForTesting;
import com.google.errorprone.annotations.concurrent.LazyInit;
import com.google.j2objc.annotations.RetainedWith;
import com.google.j2objc.annotations.WeakOuter;

import java.util.Map;
import javax.annotation.CheckForNull;

import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * Implementation of ImmutableBiMap backed by a pair of JDK HashMaps, which have smartness
 * protecting against hash flooding.
 */
@GwtCompatible(emulated = true)
@ElementTypesAreNonnullByDefault
final class JdkBackedImmutableBiMap<K, V> extends ImmutableBiMap<K, V>
{
    @VisibleForTesting
    static <K, V> ImmutableBiMap<K, V> create(int n, @Nullable Entry<K, V>[] entryArray)
    {
        Map<K, V> forwardDelegate = Maps.newHashMapWithExpectedSize(n);
        Map<V, K> backwardDelegate = Maps.newHashMapWithExpectedSize(n);
        for (int i = 0; i < n; i++)
        {
            // requireNonNull is safe because the first `n` elements have been filled in.
            Entry<K, V> e = RegularImmutableMap.makeImmutable(requireNonNull(entryArray[i]));
            entryArray[i] = e;
            V oldValue = forwardDelegate.putIfAbsent(e.getKey(), e.getValue());
            if (oldValue != null)
            {
                throw conflictException("key", e.getKey() + "=" + oldValue, entryArray[i]);
            }
            K oldKey = backwardDelegate.putIfAbsent(e.getValue(), e.getKey());
            if (oldKey != null)
            {
                throw conflictException("value", oldKey + "=" + e.getValue(), entryArray[i]);
            }
        }
        ImmutableList<Entry<K, V>> entryList = ImmutableList.asImmutableList(entryArray, n);
        return new JdkBackedImmutableBiMap<>(entryList, forwardDelegate, backwardDelegate);
    }

    private final transient ImmutableList<Entry<K, V>> entries;
    private final Map<K, V> forwardDelegate;
    private final Map<V, K> backwardDelegate;

    private JdkBackedImmutableBiMap(
            ImmutableList<Entry<K, V>> entries, Map<K, V> forwardDelegate, Map<V, K> backwardDelegate)
    {
        this.entries = entries;
        this.forwardDelegate = forwardDelegate;
        this.backwardDelegate = backwardDelegate;
    }

    @Override
    public int size()
    {
        return entries.size();
    }

    @LazyInit
    @RetainedWith
    @CheckForNull
    private transient JdkBackedImmutableBiMap<V, K> inverse;

    @Override
    public ImmutableBiMap<V, K> inverse()
    {
        JdkBackedImmutableBiMap<V, K> result = inverse;
        if (result == null)
        {
            inverse =
                    result =
                            new JdkBackedImmutableBiMap<>(
                                    new InverseEntries(), backwardDelegate, forwardDelegate);
            result.inverse = this;
        }
        return result;
    }

    @WeakOuter
    private final class InverseEntries extends ImmutableList<Entry<V, K>>
    {
        @Override
        public Entry<V, K> get(int index)
        {
            Entry<K, V> entry = entries.get(index);
            return Maps.immutableEntry(entry.getValue(), entry.getKey());
        }

        @Override
        boolean isPartialView()
        {
            return false;
        }

        @Override
        public int size()
        {
            return entries.size();
        }
    }

    @Override
    @CheckForNull
    public V get(@CheckForNull Object key)
    {
        return forwardDelegate.get(key);
    }

    @Override
    ImmutableSet<Entry<K, V>> createEntrySet()
    {
        return new ImmutableMapEntrySet.RegularEntrySet<>(this, entries);
    }

    @Override
    ImmutableSet<K> createKeySet()
    {
        return new ImmutableMapKeySet<>(this);
    }

    @Override
    boolean isPartialView()
    {
        return false;
    }
}
